Process of making elastane yarn

ABSTRACT

Described are a process for producing elastane yarn having a linear density of at least 2500 dtex by the wet spinning process and the thereby producible coarse linear density elastane yarn having a wide cross section and a low residual solvent content. The process comprises the steps of spinning an up to 35% strength by weight stable-viscosity elastane solution into a coagulation bath, washing and optionally drawing, drying by contact heating, setting, spin finishing and winding the yarn, the filaments leaving the coagulation bath passing around a diverting roller disposed just above the coagulation bath liquid, the as-spun filament linear density amounting to not more than 1% of the value of the final linear density, the jet stretch ratio being within the range from 0.5 to 50, the contact heating temperature being at least 220° C. and the contact time of the elastane yarn being at least 2 seconds.

This application is a 371 of PCT/EP99/04180, filed Jun. 17, 1999 (PCTfiling date.

The invention relates to a process for producing elastane yarn having alinear density of at least2500 dtex by the wet spinning process and thethereby producible coarse linear density elastane yarn having a widecross section and a low residual solvent content. The process comprisesthe steps of spinning an at least 25% strength by weightstable-viscosity elastane solution into a coagulation bath, washing andoptionally drawing, drying by contact heating, setting, spin finishingand winding the yarn, the filaments leaving the coagulation bath passingaround a diverting roller disposed just above the coagulation bathliquid, the as-spun filament linear density amounting to not more than1% of the value of the final yarn linear density, the jet stretch ratiobeing within the range from 0.5 to 50, the contact heating temperaturebeing at least 220° C. and the contact time of the elastane yarn beingat least 2 seconds.

BACKGROUND OF THE INVENTION

Elastane yarns are synthetic filament yarns which are produced as mono-or multifilaments—dependent on the intended use—within the lineardensity range from 11 to 2500 dtex (cf. F. Fourne:Chemiefasern/Textilindustrie 44/96; June 1994, page 392). Higher lineardensities, which extend more or less into the typical application rangeof natural rubber yarns, are perfectly interesting, however, for examplefor use as elastic undertapes for upholstery fabrics or as leg borderfor underwear and swimwear articles and also for the medical andtechnical sector.

However, the need to evaporate the spinning solution solvent in thespinning chimney imposes technical limits on producing coarse elastanelinear densities by the dry spinning process. Owing to the high lineardensity of 2500 dtex or more and the small yarn surface area of coarselinear densities, it is very difficult to evaporate sufficient spinningsolution solvent in order that the yarn may be drawn off withoutsticking together. Droplets of the spinning solution solvent stillpresent at the down-stream end of the spinning chimney lead tostuck-together filaments which, after winding onto bobbins, are nolonger satisfactorily processible off the bobbins. Furthermore, withoutincurring reduced spinning efficiency due to a reduction in the spinningspeed, it is very difficult to lower the residual solvent content in theelastane yarn to a minimum without further cost-intensive steps, such aswashing or steaming of the yarn.

By using a lower spinning speed it is possible to increase the residencetime in the dry spinning chimney and to reduce the residual level of,for example, dimethylacetamide (DMAC) solvent. However, this is at theexpense of the spinning efficiency. Nor is it possible to raise thetemperature in the spinning chimney to beyond a certain level, sincethis may give rise not only to discolourations but also to softening andmelting of the yarn. The softening range of elastane yarn varies withthe polymer composition, but is typically 180-230° C., and the meltingrange is about 250-270° C.

For this reason, in the field of the dry spinning of elastane yarn, yarnhaving a final linear density of above 2500 dtex has not been disclosedbefore. A fineness of up to 3240 dtex has been reported by GlobeManufacturing Comp. for elastane yarn reactively spun by the chemicalspinning process, and a linear density of up to 2464 dtex has beenreported by Fujibo Spandex for elastane yarn produced by wet spinning.Compare P. A. Koch: Faserstoff-Tabellen in Chemiefasern/Textilindustrie,February 1979, page 100.

In order that elastane yarn may be further processible, for example inribbon weaving, they must have a certain minimum strength. A tenacity ofat least about 0.4-0.5 cN/dtex is required in the case of coarse lineardensities to meet these demands.

However, in the case of elastane yarn having a coarse linear density ofgreater than 2500 dtex it is very difficult to achieve adequatestrength, since the higher level of residual solvents, for exampledimethylacetamide, which act as plasticizer between the polymer chains,markedly reduce the yarn's strength.

It is an object of this invention to develop elastane yarn and a processfor its production which meet the abovementioned requirements and moreparticularly to provide a high final linear density elastane yarn whichhas a low residual solvent content, high strength and high residualextensibility.

SUMMARY OF THE INVENTION

This object is achieved according to the invention by a process forproducing wet-spun elastane yarn comprising the steps of: spinning an atleast 25% strength by weight, preferably at least 30% strength byweight, stable-viscosity elastane solution into a coagulation bath toform a set of filaments, washing and optionally drawing, drying theconverged set of filaments by contact heating to form elastane yarn,setting, spin finishing and winding the elastane yarn with a finallinear density of at least 2500 dtex, preferably 3500 dtex to 20,000dtex, more preferably 4000 dtex to 15,000 dtex, the filaments leavingthe coagulation bath being passed around a diverting roller disposedjust above the coagulation bath liquid, characterized in that

a) the as-spun filament linear density is not more than 1% of the valueof the final linear density of the yarn,

b) the jet stretch ratio of the yarn is within the range from 0.3 to 50,preferably within the range from 0.5 to 50,

c) the contact heating temperature is at least 220° C., preferably atleast 230° C., especially at least 250° C., more preferably at least260° C., and

d) the contact time between the elastane yarn and the heating medium ofthe contact heating is at least 2 seconds, preferably at least 3seconds, especially at least 5 seconds.

DETAILED DESCRIPTION

Preferably, the contact heating used is a heating means featuring heatedrollers.

It is particularly advantageous to dry the elastane yarn in a heatingmeans which utilizes an electrically heated roller combined with anunheated idling roller.

The temperature at the surface of the heating roller is to beparticularly within the range from 250 to 280° C., particularlypreferably within the range from 260 to 270° C.

Particularly good results are obtained when the contact time of the yarnon the heating roller is 10 to 30 seconds, preferably 10 to 15 seconds.

It was found that the wet spinning process of the invention makes itpossible to produce elastane yarn having a final linear density of farin excess of the previously known limit of 2464 dtex whilst obtaining atenacity of distinctly above 0.4 cN/dtex, an extensibility of above 500%and a residual solvent content below 0.5% by weight.

The invention also provides elastane yarn having a final linear densityof at least 2500 dtex, especially 3500 dtex to 20,000 dtex, morepreferably within the range from 4000 dtex to 15,000 dtex, and a ribbonycross section, characterized in that the ratio of width to height in thecross section through the yarn is at least 4:1, especially at least 8:1,more preferably at least 10:1.

The elastane yarn has in particular a very low residual solvent content.The residual solvent content of the yarn is less than 1.0% by weight,preferably less than 0.5% by weight, more preferably less than 0.3% byweight at a final linear density of up to 5000 dtex.

The residual solvent content of the yarn is less than 2.0% by weight,preferably less than 1% by weight, more preferably less than 0.6% byweight, at a final linear density of 5000 to 10,000 dtex.

The residual solvent content of the yarn is less than 3.0% by weight,preferably less than 1.5% by weight, more preferably less than 1% byweight, at a final linear density of more than 10,000 dtex.

Preferred elastane yarn has a tenacity of at least 0.4 cN/dtex,preferably at least 0.5 cN/dtex.

Preferred elastane yearn has an extensibility of at least 500%,preferably at least 550%.

Of particular interest is elastane yarn which has a ribbony crosssection, the width of the yarn in cross section being greater than 1.5mm, preferably greater than 2 mm. The thickness of the yarn having aribbony cross section is greater than 0.1 mm, preferably greater than0.2, in cross section.

As the individual Examples will additionally illustrate, the disclosedparameters for the process of the invention must be adhered to so as toalso obtain continuous yarn running whilst achieving good yarn data.

If, for example, the as-spun filament linear density (ASFLD) rises tofar above 1% of the value of the final yarn linear density, broken endsmay occur on the heating roller (cf. Example 9 in Table 2). On furtherincreasing the as-spun filament linear density, the yarn can no longerbe placed on the heating roller, since yarn is constantly breaking onthe heating roller (cf. Example 10 in Table 3).

To obtain a yarn tenacity of at least 0.4 cN/dtex, the jet stretch ratioshould be at least 0.5. A lower jet stretch ratio may in certaincircumstances not provide the desired yarn tenacity (cf. Examples 11 and12 in Table 3). Similarly, the setting temperature and the contact timefor the yarn on the heating roller plays an essential part in relationto the yarn tenacity and the remaining residual solvent content in thecase of coarse linear density elastane yarn.

As is discernible from Table 4, even a setting temperature of 260° C.and a contact time of below 5 seconds may in certain circumstances notprovide optimal yarn strength in the case of elastane yarn having alinear density of 3000 dtex (cf. Example 20 in Table 4). Only a contacttime of not less than about 5 seconds and a setting temperature of least250° C. will provide in such a case a yarn tenacity of 0.4 cN/dtex ormore (cf. Example 19 in Table 4). In the case of coarser lineardensities than 3000 dtex, the contact time for the elastane yarn on theheating roller and possibly also the setting temperature may have to beraised in certain cases to obtain a particular yarn strength. Forinstance, a linear density of 7381 dtex requires a contact time of 14.8seconds in the case of setting temperatures of 260/265/270° C. for zones1-3 of the heating roller to obtain a yarn tenacity of 0.67 cN/dtex (cf.Example 1 and Table 4, Example 21).

In general, the elastane yarn can be set on one or else two pairs ofelectrically heated rollers, for example in accordance with anarrangement as in FIGS. 1a-1 d of OPI document DE 195 04 316. In thepresent case, it is particularly the arrangement of FIG. 1a of DE 195 04316, featuring an electrically heated roller and an adjustable idlingroller, which has proven to be particularly advantageous. To set thetemperature profile mode on the heating roller, use is preferably madeof godets having radiative heating elements and adjustable shrouds asare fundamentally known in the art.

It is important for the drawing of the elastane yarn to take placebetween the washing and the drying of the yarn. Otherwise, nonuniformyarn material having reduced quality, linear density fluctuations, i.e.an increase in the coefficient of variation of linear density, strengthand extensibility, is observed.

The process of the invention preferably utilizes elastane polymerscontaining at least 85% by weight of segmented polyurethane.

Segmented polyurethanes are for example segmented polyurethanes based onpolyethers, polyesters, polyetheresters, polycarbonates or mixturesthereof.

Elastane yarn according to the invention is used both in the textile andin the nontextile sector, for example as elastic undertapes forupholstery fabrics or as leg border for underwear and swimwear articlese.g. disposable diapers, and also for articles from the medical andtechnical sector.

In the examples hereinbelow, parameters reported include the as-spunfilament linear density.

The as-spun filament linear density (ASFLD) is calculated as follows:${ASFLD} = {\frac{{F \times K \times 0.94 \times 100}\quad}{A \times Z}({dtex})}$

F=pumpage rate (ccm/min)

K=concentration of spinning solution (% by weight)

A=coagulation bath speed (m/min)

Z=number of jet holes

The jet stretch ratio (V) is defined as the ratio of the take-off speed(A) to the extrusion speed (S)$V = \frac{A( {m\text{/}\min} )}{S( {m\text{/}\min} )}$

The extrusion speed (S) is given by:$S = \frac{4 \times {F( {m\text{/}\min} )}}{Z \times d^{2} \times \pi \times 100}$

F=pumpage rate (ccm/min)

Z=number of jet holes

d=jet hole diameter (cm)

The take-off speed (A) corresponds to the speed of the yarn afterleaving the heating roller.

The examples which follow serve to illustrate the invention. Percentagesare based on the weight of the finished elastane yarn, unless otherwisestated.

The determination of the yarn tenacity (in cN/dtex) and of the ultimatetensile strength extension (in %) was effected on the lines of thestandard DIN 52815, the yarn data being measured, given the coarselinear densities, using a large-scale instrument from Wolpert, having ameasuring range of up to 200 newton per yarn.

EXAMPLES Example 1

A 29.5% strength by weight elastane spinning solution prepared accordingto Example 7 of DE-05 4 222 772, the spinning solution having beenpretreated with 0.5% of diethylamine at 140° C. for about 10 min andhaving a spinning viscosity of 22 Pa.s measured at 50° C., was spunthrough two 397 hole jets having jet hole diameters of 0.1 mm into acoagulation bath containing 25.2% strength DMAC-water mixture at 85° C.The ends were converged via a yarn holder disposed at a distance of 500mm from the jets, taken off at 80 m/min via a diverting roller disposedjust above the coagulation bath liquid, coalesced and washed in a washbath featuring a pair of wash rollers featuring a press roller for theends and at 120 m/min set on a heating roller and spin finished, and thefolded yarn was wound up on a bobbin. The pumpage rate of the spinningpump supplying the two jets was 319.4 ccm/min. The as-spun filamentlinear density (ASFLD) is 13.9 dtex, which corresponds to 0.19% of thevalue of the final yarn linear density. The jet stretch ratio was 1.6.

The yarn was transported via a heating roller (subdivided into differenttemperature zones) combined with an unheated idling roller, thetemperatures being 260° C. in zone 1,265° C. in zone 2 and 270° C. inzone 3, by wrapping the two rollers 52 times, which corresponds to acontact time of 14.8 seconds.

The elastane yarn obtained had a final linear density of 7381 dtex, atenacity of 0.67 cN/dtex, an extensibility of 636% and a residual levelof 0.16% for the DMAC spinning solution solvent. The elastane yarn ispresent in the form of a continuous-surface ribbon. Ribbon width isabout 5 mm and ribbon thickness 0.42 mm.

Examples 2-6

Table 1 below summates further Examples (Nos. 2-6) relating to theproduction of coarse linear density elastane yarn by the process of theinvention. In all cases, an elastane polymer having the chemicalcomposition of Example 1 was dissolved in DMAC and a spinning solutionwas spun as described therein. The resulting yarns were washed, set,spin finished and wound up, all steps being carried out as described inExample 1.

In all cases, yarn tenacity was at least 0.4 cN/dtex and yarnextensibility at least 500%. The residual DMAC content of the yarn wasbelow 0.30% by weight based on polymer solids. According to Table 1, itis possible to produce elastane yarn of 10,000 dtex or more.

TABLE 1 AFSLD as % age Heating yarn of final Residual Number PumpageCoagulation roller linear yarn Jet Yarn Extensi- DMAC of Jets rate bathspeed speed ASFLD density linear stretch Tenacity bility Content No. jetholes Ø mm cc m/min m/min. m/min dtex dtex density ratio cN/dtex % % 1 2× 397 0.1 319.5 80 120 13.9 7381 0.19 1.6 0.67 636 0.14 2 397 0.1 180.580 120 15.8 4178 0.38 1.4 0.67 617 0.19 3 2 × 397 0.1 234.5 60 120 13.65402 0.25 1.6 0.63 718 0.16 4 2 × 397 0.1 281.5 60 120 16.4 6448 0.251.3 0.61 679 0.18 5 4 × 300 0.1 349.7 50 120 16.2 8081 0.2 1.3 0.55 5830.21 6 4 × 300 0.1 467.5 50 120 21.6 10,801 0.2 1 0.54 562 0.23

Examples 7 and 8, and Comparative Example 9

A portion of the spinning solution of Example 1 is spun into 7300 dtexelastane yarn as described in Example 1, except that the two 397 holejets are replaced by a single jet of 175-350 holes and a bore diameterof 0.15 mm. The speed in the coagulation bath was 50 instead of 80n/min. As s discernible from Table 3, problems in the form of brokenends keep on occurring in the setting process on the heating rollerwhenever the value of the as-spun filament linear density is more than1% of the final yarn linear density (cf. Examples Nos. 7 and 8, whichare according to the invention and Example 9 which is not according tothe invention, in Table 2), i.e. whenever the as-spun filament lineardensity is to high.

TABLE 2 ASFLD Final as % age Heating yarn of final Number PumpageCoagulation roller linear yarn Jet Yarn Extensi- of Jets rate bath speedspeed ASFLD density linear stretch tenacity bility Yarn No. jet holes Ømm ccm/min m/min m/min dtex dtex density ratio cN/dtex % running 7 3500.15 319.4 50 120 50.6 7301 0.7 1 0.64 644 o.k. 8 250 0.15 319.4 50 12070.9 7330 1 0.7 0.61 603 o.k. 9 200 0.15 319.4 50 120 88.6 7298 1.2 0.60.563 617 occas- ional breakages on heating roller

Examples 10-14

A further portion of the spinning solution of Example 1 is spun into7300 dtex elastane yarn as described in Example 1, except that the 397hole jets used have a finer bore diameter (0.08 instead of 0.1 mm) insome cases and the filaments are spun at lower speeds in the coagulationbath (25-40 m/min instead of 80 m/min). As is discernible from Table 3,jet stretch ratios of less than 0.5 no longer ensure an adequate yarnstrength of at least 0.4 cN/dtex (cf. Examples Nos. 10 and 11 in Table3).

TABLE 3 ASFLD Final as % age Heating yarn of final Number PumpageCoagulation roller linear yarn Jet Yarn Extensi- of Jets rate bath speedspeed ASFLD density linear stretch tenacity bility No. jet holes Ø mmccm/min m/min m/min dtex dtex density ratio cN/dtex % 10 2 × 397 0.08319.4 25 120 44.6 7385 0.6 0.3 0.33 633 11 2 × 397 0.08 319.4 35 12031.9 7309 0.4 0.4 0.39 674 12 2 × 397 0.08 319.4 40 120 27.9 7294 0.40.5 0.44 666 13 2 × 397 0.1 319.4 25 120 44.6 7390 0.6 0.5 0.41 641 14 2× 397 0.1 319.4 35 120 31.9 7288 0.4 0.7 0.52 682

Examples 15-21

Another portion of the spinning solution of Example 1 is spun from a 397hole jet into 3000 dtex elastane yarn as described in Example 1, exceptthat the setting conditions for the elastane yarn on the heating rollerare varied according to FIG. 1a. The elastane yarn is passed over theheating roller whilst temperatures and contact times are being varied.Temperature profiles of 230-270° C. are set. Yarn contact time on theheating roller can be varied between about 4.7 seconds and about 9.8seconds by varying the number of wraps (17 yarn wraps correspond to 4.7seconds). Table 4 reveals that yarn capabilities greater than 0.4cN/dtex are obtained only at setting temperatures from about 250° C. andcontact times of at least 5 seconds (cf. Examples 15 to 17 and 19 inTable 4).

TABLE 4 Speed on Temperature heating roller of heating roller in ° C.Contact time Linear density Tenacity Extensibility No. m/min Zone 1 Zone2 Zone 3 sec dtex cN/dtex % 15 120 230 240 245 4.9 3070 0.31 533 16 120230 240 245 9.8 3065 0.37 579 17 120 250 250 250 4.7 3044 0.38 566 18120 250 250 250 5.1 3071 0.41 613 19 120 250 255 260 4.7 3075 0.39 57420 120 260 265 270 5.1 3028 0.51 649 21 120 265 270 270 9.8 3019 0.71685

We claim:
 1. Process for producing wet-spun elastane yarn comprising thesteps of: spinning an at least 25% strength by weight, stable-viscosityelastane solution into a coagulation bath to form a set of filaments,washing and optionally drawing, drying the converged set of filaments bycontact heating to form elastane yarn, setting, spin finishing andwinding the elastane yarn with a final linear density of at least 2500dtex, the filaments leaving the coagulation bath being passed around adiverting roller disposed just above the coagulation bath liquid,wherein a) the as-spun filament linear density is not more than 1% ofthe value of the final linear density of the yarn, b) the jet stretchratio of the yarn is within the range from 0.3 to 50, c) the contactheating temperature is at least 220° C., and d) the contact time betweenthe elastane yarn and the heating medium of the contact heating is atleast 2 seconds.
 2. Process for producing elastane yarn according toclaim 1, wherein the contact heating used is a heating means featuringheated rollers.
 3. Process for producing elastane yarn according toclaim 1, wherein the heating means utilizes an electrically heatedroller combined with an unheated idling roller.
 4. Process for producingelastane yarn according to claim 1, wherein the temperature at thesurface of the heating roller is within the range from 250 to 280° C. 5.Process for producing elastane yarn according to claim 3, wherein thecontact time of the yarn on the heating roller is 10-30 seconds. 6.Process for producing elastane yarn according to claim 1, wherein thefinal linear density of the elastane yarn is within the range from 3500dtex to 20,000 dtex.
 7. Process of claim 1, wherein said strength is atleast 30% by weight, said stretch ratio is in the range of 0.5 to 50,said temperature is at least 250° C. and said contact time is at least 5seconds.
 8. Process of claim 4, wherein said temperature at the surfaceof said heating roller is from 260 to 270° C.
 9. Process of claim 5,wherein said linear density is in the range of 4000 dtex to 15,000 dtex.